This invention relates to an apparatus and method for compiling printed sheets in a bindery process and which is characterized by the ability to accurately detect a missing or incorrectly fed sheet.
The use of a collating system to build book-block sets which are then finished and bound has been a conventional practice in the bookmaking industry. These systems typically support the sheets or signatures in either a vertical or inclined stack, and a number of successively arranged feeders successively drop the sheets onto a collating chain so as to progressively build a book-block set along the chain. The collated book-block set is then finished, i.e. trimmed and bound. The success of this collating system is dependent upon the systematic placement of the proper sheet onto the collating chain in the right sequence. However, problems often develop during collating which prevent the formation of a proper book-block set. For example, a feeder may misdeliver and deposit more than one sheet onto the collating chain. Also, an incorrect sheet may be placed in a feeder, or a proper sheet may be placed incorrectly in the feeder, such as upside down, and the feeder will then deliver the wrong or misaligned sheet to the chain. Still further, the feeder sheet may misfeed completely and not even deliver a sheet, with the result that a sheet in the book-block set is missing.
Certain quality control measures have heretofore been implemented that have helped to alleviate these problems. One of the more successful quality control measures implemented to date has been the use of a mechanical caliper associated with each conveyor chain. These calipers typically employ a mechanical feeler gauge which is calibrated to measure the thickness of the several sheets of a collated set. Thus, if a feeder malfunctions and feeds a duplicate number of sheets or does not feed any sheets, the feeler gauge measures an improper thickness and signals a control device that there has been a misfeed. The control device, in turn, prevents the further finishing of that particular book-block set which is then separated from those book-block sets which are determined to be proper.
Unfortunately, the use of mechanical calipers does not indicate all possible errors. For example, a mechanical caliper cannot detect when a wrong sheet has been fed through a feeder, and also it cannot detect if a sheet has been incorrectly fed, i.e. incorrect pagination. In both these cases, the caliper would detect that sheets of proper thickness had been fed through a feeder, but the caliper would not detect that one was upside down or was the wrong sheet for that particular feeder.
It is accordingly an object of the present invention to provide an apparatus and method for compiling sheets fed onto a collating chain and which overcomes the above noted deficiencies of the prior art practices.
It is a more particular object of the present invention to provide an apparatus and method for scanning the sheets fed onto a collating chain from successively arranged feeders, and which is able to detect an incorrectly fed sheet as well as a missing sheet.